The present invention pertains to ranging systems for controlling various functions in a photographic apparatus. More specifically, it relates to a method and apparatus for controlling photographic focusing, exposure and flash firing functions according to camera-to-subject range.
In the photographic arts, various systems have been proposed for transmitting energy to an object and detecting the reflected energy. Characteristics of the transmitted and reflected energy are utilized for deriving a signal representative of the object-to-system distance. This signal is used for controlling a variety of photographic operations including focusing, flash firing and exposure.
One example of such a ranging system is described in U.S. Pat. No. 4,199,246 entitled "Ultrasonic Ranging System For a Camera", issued to J. Muggli, on Apr. 22, 1980. For determining object distance, the elapsed time between transmission and receipt of an ultrasonic signal, which is bounced off the object, is utilized. The ultrasonically derived ranging signal is used for driving a lens assembly to a correct focal position for focusing purposes.
Another known ranging system for cameras uses the concept of triangulation as a means for deriving subject range. An example of this is employed in Canon's AF 35M camera, wherein an infrared-emitting diode shifts laterally, during a measuring cycle, relative to a fixed sensor cell which monitors the maximization of the reflected infrared radiation. The distance the emitter diode travels to provide such maximization is related to the subject distance and a range signal is derived for adjusting focusing of a lens arrangement. U. S. Pat. Nos. 3,736,057 and 4,150,888 are also exemplary of cameras employing triangular type range systems.
The foregoing ranging techniques are also utilized for flash control as, for example, with use of a "follow-focus" mechanism. Mechanisms of this kind utilize a derived range signal or the resultant lens position for locating a preselected aperture value, in operative relation to the exposure path, for providing proper exposure during flash firing. Thus, a scanning shutter blade mechanism may be stopped at an aperture value corresponding to the camera-to-subject distance. Reference is made to U.S. Pat. No. 3,977,014 entitled "Follow Focus Exposure Control System With Improved Uniform Trim Control", by P. Norris, issued Aug. 24, 1976, in common assignment herewith for an example of such a follow-focus mechanism.
In other scanning shutter systems, the opening shutter blade movement is not stopped at the selected exposure aperture. Instead, the time of flash firing is varied in response to subject range so as to dynamically select an appropriate aperture, which for a given strobe output, will produce adequate lighting of the subject at that measured range. Significantly, the duration of the strobe light in such system is short in comparison to shutter blade scan time. Hence, the aperture defined by the shutter blades at the instant of strobe firing, for practical purposes, constitutes the effective aperture at which the flash exposure occurs. Such systems are more fully described in U.S. Pat. No. 3,478,660 entitled "Photographic Apparatus With Flash Exposure Control System", by E. Land, issued Nov. 18, 1969, and U.S. Pat. No. 4,188,103 entitled "Range Synchronized Flash Photographic Apparatus and Method For Achieving Optimum Exposure", issued Feb. 12, 1980; all commonly assigned herewith.
The above described range dependent flash control systems, while highly successful, generally utilize relatively costly ranging units and fail to account for the variations in light reflectivity typically found in photographic scenes.
On the other hand, many flash control systems, such as for example photoresponsive quench control strobe systems, are heavily dependent upon scene reflectivity. Likewise wink type systems, such as described in U.S. Pat. Nos. 3,465,656, 3,418,904 and 3,583,299, which employ a preliminary flash or wink for flash control, are also sensitive to scene reflectivity. Unfortunately, the wide range of reflectivity encountered in some photographic scenes results in poor regulation in such instances.
Advantageously, it has been found that the use of non-visible light, i.e., infrared, for evaluation during flash exposure reduces the extreme variation of reflectivity as described in U.S. Applications, Ser. No. 127,120 filed Mar. 4, 1980 abandoned and Ser. No. 156,198 filed Dec. 31, 1979 U.S. Pat. No. 4,315,075 and commonly assigned herewith. PG,5
In photographic ranging, infrared illumination has been conventionally utilized to avoid disturbance of the scene. In time based range systems and triangulation range systems, which are not dependent upon the total amount of reflected energy, the use of such non-visible light has no basic effect on the measured range. Likewise, the infrared illumination employed in U.S. Pat. No. 3,937,574 is of no effect with regard to ranging since this arrangement employs a novel, dual detector system to eliminate all reflectivity values from the resulting range signal.
Finally, U.S. Pat. No. 3,173,347 teaches the use of an infrared light source for ranging in an intensity evaluating system to the advantage as stated therein that the camera exposure control need not be disabled for flash, the system is useful at low ambient levels, and the subject is not aware of such illumination. The latter system utilizes a special source of infrared illumination with a special photocell to provide a range signal responsive to the intensity of reflected radiation from the subject. Hence, this patent employs infrared illumination for conventional reasons, fails to recognize any improvement in reflection variation, and employs a complicated dual system to achieve its range signal.